a. Field of the Invention
This invention relates to the creation of identification marks of other visible or invisible (but detectable) indicia on diamonds, for the purposes of quality control, consumer brand identification, security or any other purpose requiring identification of a stone.
b. Description of the Pertinent Technical Art
Luxury and consumer goods alike are most often provided with an identifying mark from which the source of the goods can be identified. This is especially important in the case of a product whose quality and value can only be determined by specially skilled workers. Such identifying marks must be on the goods in a permanent form. On the other hand, the indicia should not impair the value of the goods in any way.
In the case of precious stones such as diamonds, there has long been a need for a reliable method by which the identity of a stone could be uniquely determined. Such a method would aid in locating and recovering specific pieces of lost or stolen jewelry. Furthermore, where diamonds are loaned on a temporary basis, as is not uncommon, permanent indicia on the stone would facilitate ensuring that the returned stone is identically the same as the loaned stone.
In addition, such detection systems or indicia could serve to indicate the level of quality or craftsmanship of the faceting, cutting and polishing of the stone. In essence, a permanent mark or detectible indicium on a diamond may serve as a hallmark or trademark in much the usual fashion, i.e., as an identification of source. Such a mark may be employed in dispelling the common misunderstanding that diamonds are essentially fungible, for any given weight, color and clarity. In fact, the quality of the gemstone may be markedly affected by the skill and care of the stoneworker in the selection, sawing, girdling, cutting and polishing processes.
There have been devised a number of processes for marking diamonds, such as are disclosed in U.S. Pat. Nos. 4,467,172 and 4,392,476, which entire disclosures are incorporated herein by reference. In each of these patents, lasers are disclosed for creating focussed spots of laser energy on or in the diamond to be marked, wherein the desired indicia are formed by creating series or patterns of dots with such focussed spots of energy.
The aforementioned laser marking systems employ YAG or Nd:YAG lasers operating at 1.06 microns wavelength, alone or in conjunction with frequency doublers. Thus the disclosed laser radiation incident on the diamond is at either 1.06 or 0.532 micron wavelength. As recognized in U.S. Pat. No. 4,467,172, laser energy at 0.532 microns wavelength can penetrate the surface of a diamond and can heat and vaporize portions of material below, as well as at, the diamond surface. This penetration of energy is undesirable and poses undue risks of fracturing the stone as a result of internal heating of the crystal structure. The prior art systems thus include complex arrangements to precisely control the amount of laser energy delivered so as to prevent damage to the diamonds being thus marked.
In addition, because diamond is substantially transparent or transmissive at the aforementioned wavelengths, such prior diamond marking processes generally involve the application of energy absorbing coatings such as carbon black to the surface to be marked, further complicating the procedure.
Moreover, since the indicia are formed by multiple spots, complex and expensive computer-driven X-Y tables are provided in the aforementioned prior art systems for accurately positioning the diamond with respect to the focussed spot of laser energy to be next applied. The need to create numerous spots to form a single mark further causes the prior art marking processes to be relatively slow in operation.